docs: def send(self, envelope):
          """Sends an *envelope*."""
          if not self.is_connected:
              self._connect()
  
          msg = envelope.to_mime_message()
          to_addrs = [envelope._addrs_to_header([addr]) for addr in envelope._to + envelope._cc + envelope._bcc]
  
          return self._conn.sendmail(msg['From'], to_addrs, msg.as_string())